arXiv:2509.06037v3

Polynomial entropy of induced homeomorphisms on Ck(S1)C_k(\mathbb{S}^1) and Ck([0,1])C_k([0,1])

Maša Đorić, Jelena Katić

math.DS37B4054F1637A35

Abstract

We compute the polynomial entropy of Ck(f)C_k(f) where ff is any circle or interval homeomorphism.

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Audited against arXiv v3

Not a correctness certificate. A “Correct” result may include yellow typos or minor formal corrections that do not affect substantive soundness. It means this audit found no unresolved substantive error under the stated criteria; it does not replace expert scrutiny or formal verification.

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Detailed mathematical audit

Generated August 18, 2026
01Statements2 reported findingsContains wrong statements

The circle alternative in Theorem 2 is false for orientation-reversing involutions: a reflection is not conjugate to a rotation, but its induced map has polynomial entropy zero rather than 2k2k. The rotation-conjugate zero-entropy branch is correct.

Theorem 2 · circle caseIncorrect

A circle reflection contradicts the stated dichotomy

Pages 1–2 and 8 · Theorem 2 and its proof · arXiv:2509.06037v3

The theorem claims that every circle homeomorphism not conjugate to a rotation satisfies hpol(Ck(f))=2kh_{\mathrm{pol}}(C_k(f))=2k. Let ff be a reflection of S1S^1. Orientation type is invariant under conjugacy, so this orientation-reversing map is not conjugate to any rotation. But f2=Idf^2=\operatorname{Id}, hence Ck(f)2=Ck(f2)=Id.C_k(f)^2=C_k(f^2)=\operatorname{Id}. The separated-set cardinalities for Ck(f)C_k(f) are therefore bounded independently of the orbit length once the two iterates have been included, and hpol(Ck(f))=0h_{\mathrm{pol}}(C_k(f))=0. This is a counterexample for every k1k\geq1. A substantive repair must change the circle statement, for example by imposing orientation preservation; no local proof correction can make the printed dichotomy true.

Reviewed manuscript, version 3
Theorem 2 · rotation branchCorrect

Conjugacy to a rotation gives zero polynomial entropy

Pages 3 and 8 · Lemma 3 and proof of Theorem 2 · arXiv:2509.06037v3

A rotation of S1S^1 is an isometry, and its induced action on Ck(S1)C_k(S^1) preserves the Hausdorff metric. Polynomial entropy is invariant under topological conjugacy, while an isometry has bounded separated-set growth. Thus the stated zero-entropy conclusion in this branch follows. The printed proof of Lemma 3 has a repairable inference defect recorded separately in the proof audit, but the lemma and this branch are correct by the verified inverse-isometry argument given there.

02Proofs4 reported findingsContains incorrect or incomplete proofs

The proof discards the orientation-reversing case by passing to f2f^2, although this loses the distinction needed by the theorem and admits the reflection counterexample. Independently, Proposition 7 relies on the false assertion that taking boundaries is 11-Lipschitz in Hausdorff distance. Lemma 3 contains a local false inference but has a fully verified repair.

Proof of Theorem 2 · orientation reductionIncorrect as written

Passing to the square does not preserve the theorem's case distinction

Page 8 · first paragraph of the proof of Theorem 2 · arXiv:2509.06037v3

The proof says that one may assume ff orientation-preserving because f2f^2 is orientation-preserving and hpol(Ck(f2))=hpol(Ck(f))h_{\mathrm{pol}}(C_k(f^2))=h_{\mathrm{pol}}(C_k(f)). The entropy identity is valid, but it does not imply that the printed hypothesis branch for f2f^2 is the same as that for ff. For a reflection, f2=Idf^2=\operatorname{Id} is conjugate to a rotation while ff is not, so the argument gives entropy zero and contradicts the theorem's claimed 2k2k. Repair classification: No repair supplied. The theorem itself must be restricted or its zero-entropy alternative enlarged.

Proposition 7Incorrect as written

The boundary map is not 11-Lipschitz

Pages 7–8 · proof of Proposition 7, after Equation (2) · arXiv:2509.06037v3

The lower bound is deduced from the assertion that π(K)=K\pi(K)=\partial K is 11-Lipschitz from Ck(S1){S1}C_k(S^1)\setminus\{S^1\} to F2k(S1)F_{2k}(S^1). This assertion is false for k2k\geq2. Inside an embedded arc identified with [0,1][0,1], take K=[0,1],Kε=[0,1/2][1/2+ε,1].K=[0,1],\qquad K_\varepsilon=[0,1/2]\cup[1/2+\varepsilon,1]. Then dH(K,Kε)=ε/2d_H(K,K_\varepsilon)=\varepsilon/2, whereas Kε\partial K_\varepsilon contains points near 1/21/2 whose distance from K={0,1}\partial K=\{0,1\} stays close to 1/21/2. Consequently the displayed inequality comparing Hausdorff distances of the lifts with those of their boundaries can fail. Proposition 8 repeats the same argument, so the printed lower-bound proofs for the nonzero-entropy branches of Theorem 2 are not established by this route. Repair classification: No repair supplied; a different separated-set construction or another verified lower-bound argument is required.

Reviewed manuscript, version 3
Lemma 3Incorrect as written

The reverse Hausdorff inequality does not follow from an arbitrary distant pair

Page 3 · final two sentences of the proof of Lemma 3 · arXiv:2509.06037v3

From s<dH(A,B)s<d_H(A,B), the proof selects aAa\in A and bBb\in B with d(a,b)>sd(a,b)>s and concludes that f(A)⊄U(f(B),s)f(A)\not\subset U(f(B),s). One distant pair does not establish that f(a)f(a) is farther than ss from every point of f(B)f(B), so this inference is false. Repair classification: Verified repair. The preceding argument already proves dH(f(A),f(B))dH(A,B).d_H(f(A),f(B))\leq d_H(A,B). Apply the same inequality to the inverse isometry f1f^{-1} and the sets f(A),f(B)f(A),f(B) to obtain the reverse inequality. This proves the lemma and repairs every later use without changing any statement.

Proposition 8Minor formal correction

The regularity hypothesis is mismatched with Theorem 2

Page 8 · statement of Proposition 8 and final sentence of the proof of Theorem 2 · arXiv:2509.06037v3

Proposition 8 is printed for an interval diffeomorphism, but Theorem 2 is stated for every interval homeomorphism and invokes Proposition 8 directly. The argument in Proposition 8 uses only that an interval homeomorphism is monotone and that its square is increasing; it uses no differentiability. Replace `diffeomorphism' by `homeomorphism' in Proposition 8. This uniquely determined local change fixes the hypothesis mismatch, although it does not repair the separate false boundary-map step inherited from Proposition 7.

03Novelty0 reported findingsNo non-novelty findings

No non-novelty findings.

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Paper
arXiv:2509.06037v3
Authors listed
Maša Đorić, Jelena Katić
Audit date
August 18, 2026
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